Many drugs can degrade and lose their efficacy through hydrolysis, or otherwise stated by reacting
with water. In a large number of situations, the moisture diffuses from the outside environment through
the film and into the product. A package engineer can select a different type of film to create different
levels of barrier to guard against water diffusion. Mono-layer films, such as those manufactured from
PVC, polyester, and polypropylene, offer only a very basic level of moisture vapor protection. In moisture
sensitive applications, successfully protecting the drug requires some type of multiple layer structure
barrier film.